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Universidad de Puerto Rico en Humacao Departamento de Física y Electrónica
Año Académico 2011-2012
Número 7
RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Tabla de Contenido
Composite Nanofibers of Electroactive Polymers Prepared Via Electrospinning.
William Serrano Advisor: Nicholas Pinto
4
Devices and Sensors Based on PVDF-TrFE/SWNT’s Composites. Manuel Bonilla
Advisors: Idalia Ramos and Nicholas Pinto
5
Electrical Characterization of CVD Graphene. Yarelys Dávila Advisor: Nicholas Pinto 6
Electrical Characterization of Field Effect Transistors Made From C-nanotubes Covered with
Poly(3-hexylthiophene). Luis O. Pomales Advisor: Nicholas Pinto
7
Observation Report for the Year 2009, Humacao University Observatory. D. Centeno,
L. Rivera-Rivera, E. Franco, V. Maldonado, M. De Jesús, R.A. Rodríguez, A. J. Sosa,
M. Rosario, M. Díaz Advisors: R. J. Muller and J. C. Cersosimo
7
Study of Formation of Polymeric Fibers Containing Magnetic Nanoparticles.
Jean Carlo Serrano Advisor: Rogerio Furlan
8
Study of Formation of Polyvinylidene Fluoride Nanofibers Using Acetone as Solvent.
William Serrano García Advisor: Rogerio Furlan
9
Writing Polymeric Patterns Using an Atomic Force Microscope. Godohaldo J. Pérez Medina
Advisors: Rogerio Furlan and Luis G. Rosa
10
Study of Ionized Hydrogen in the Carina Region. Milennys Velázquez Flores, Clarissa
Vázquez Colón, Grace Fontanes, Milzaida Sanabria Advisor: J. C. Cersosimo
11
Nanoscale Fabrication of the Ferroelectric Polymer Poly(vinylidene Fluoride with Trifluoroeth-
ylene) P(VDF-TrFE) 75:25 Thin Films by Atomic Force Microscope Nanolithography.
Omar Vega, David Delgado, Freddy Wong, Rosette González Advisor: Luis G. Rosa
12
RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Page 2 Número 7
Número 7 Page 3 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Weak Screening of a Large Dipolar Molecule adsorbed on Graphene. Lingmei Kong, G.J. Pérez
Medina, J.A. Colón Santana, F. Wong, M. Bonilla Advisors: Luis G. Rosa, D.A. Colón Amill,
L. Routaboul, P. Braunstein, B. Doudin, Chang-Mook Lee, Jaewu Choi, Jie Xiao and P.A.
Dowben
13
The Effect of Thermal Annealing on the Efficiency of Semitransparent Organic Solar Cells.
Gabriel Calderón, Héctor Carrasco Rodríguez, Jorge Marcano Bermúdez
Advisor: Josee Vedrine-Pauléus
14
Radiation Hazard on Long-Haul Airplane Flights. V. De La Rosa
Advisor: Ernesto P. Esteban
15
On the Carcinogenic Effects of Galactic Cosmic Rays at Low Earth Orbit and Deep Space.
P. Agosto Advisor: Ernesto Esteban
16
Polyaniline-Carbon Nanotubes Composite Actuator. Sabrina Rosa, Carlos Camargo
Advisors: Idalia Ramos and Eva Campo
17
Aluminum Nitride Nanofibers Fabricated Using Electrospinning and Nitridation.
Xenia Barbosa Advisors: Idalia Ramos, Eva Campo and Jorge Santiago
18
Synthesis of Electrospun Indium Gallium Nitride Nanofibers. Joshua L Robles García
Advisor: Idalia Ramos
18
Renovable Energy From Waves Using Magnetic Induction. Carlos Calderón, Kenneth Benítez
Advisor: Juan A. González Sánchez
19
Approaching an Organic Semi-metal: Electron Pockets at the Fermi Level for a Pbenzoqui-
nonemonoimine Zwitterion. Zhengzheng Zhang, José Alvira, Omar Vega, Gerson Díaz,
Julian Velev Advisors: Luis G. Rosa, Lucie Routaboul, Pierre Braunstein, Bernard Doudin,
Yaroslav B. Losovyj and Peter A. Dowben
20
La Edad del Cráter de Giordano Bruno. Luis O. Pomales Advisors: Abraham Ruiz y
William A. Bruckman
21-23
Número 7
Composite Nanofibers of Electroactive Polymers Prepared
Via Electrospinning
Page 4 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
William Serrano
Advisor: Nicholas J. Pinto
Nanofibers of poly(vinylidene fluoride-trifluoroethylene)- PVF2-TrFE, a ferroelectric copolymer, blended
separately with each of the following conducting polymers, PEDOT-PSSA, PANi and P3HT were prepared
in air at room temperature using the electrospinning technique. The presence of the conducting polymer
assisted in the fabrication of PVF2-TrFE fibers at surprisingly low polymer concentrations in solution. UV/
VIS spectroscopy showed that the conducting polymer was uniformly incorporated into the PVF2-TrFE
solution with no polymer segregation. In the electrospinning process it is known that the net charge density
in the electrospinning jet and reduced surface tension lead to uniform fibers without beads. Scanning electron
microscope images indeed show a reduction in the beading effect and an increase in fiber formation when a
conducting polymer is incorporated into the composite. The fiber diameters increased with increasing PVF2
-TrFE concentrations. These electroactive polymers have the potential of combining charge storage with
conducting properties. Simple devices like diodes and field effect transistors have been fabricated from the
composite nanofibers and tested successfully. This work presents a quick, cheap and reliable way of
preparing functional polymer composite nanofibers under ambient laboratory conditions and in device
fabrication.
Figure 1: SEM images of electrospun fibers of (a) 13wt% PVF2-TrFE; (b) 13wt% PVF2-TrFE/P3HT; (c) 15wt%
PVF2-TrFE; (d) 15wt% PVF2-TrFE/P3HT. All images have the same magnification and the scale bar in each
represents 10 mm.
Devices and Sensors Based on PVDF-TrFE/SWNT’s Composites
Manuel Bonilla
Advisors: Idalia Ramos and Nicholas Pinto
RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Page 5 Número 7
Sensor devices were prepared using PVDF-TrFE/SWNT’s composite and compared with a pure SWNT’s
sensor. Current as function of time measurement at room temperature shows an improved sensitivity a
faster response time in the presence of acetone for the composite resistor device that was fabricated putting
the composite solution between two gold electrodes in n doped Si substrate. The pure SWNT’s resistor
produced a faster response time that the composite in the presence of NO2. Schottky diodes were prepared
with the PVDF-TrFE/SWNT’s composite and the n doped Si. Successful rectification was obtained and
changes in the turn on voltage and in the Ion/Ioff ratio were observed as the diode was in the environments
of different gases. The composite improve the sensitivity of the devices that can be prepared fast and can
be used to prepare a device with both diode and resistor functionalities. These sensor and the diodes can be
reused after gas removal.
R/R
N2
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
T(s)
0 500 1000 1500 2000 2500 3000
R/R
N2
0.2
0.3
0.4
0.5
0.6
0.7
0.8
(a)
(b)
Fig. 1.Normalized resistance of individual sensors switching the gas ambience between (a) N2 and acetone (b) N2 and N02. PVDF-TrFE/ SWNT’s is in black and SWNT’s. in red. The arrows indi-cate the moment when the specified gas was introduced
Figure 1 shows the normalized resistance of the pure
SWNT and the composite PVDF-TrFE/SWNT sensors
in the presence of acetone and NO2 gases. The
response to acetone is rapid and true saturation can be
observed, while for NO2 the sensor does not appear to
saturate in the 300s time interval of the measurements.
Nevertheless, in the four cycles presented in Figure 1,
there is reproducibility. The response times of these
sensors is presented in Table 1 and shows that compo-
site sensors are much faster than pure SWNT sensor for
acetone. This could be due the presence of the polymer
that speeds gas entry into the fiber. From Figure 1 we
see that acetone increases the resistance due to polymer
swelling while NO2 decreases it and could be related to
the doping effect that NO2 has on organic materials eg.
graphene[2].
FE/SWNT were fabricated and tested in acetone and
NO2. The composite sensors had a faster response time
in acetone compared to NO2. A Schottky diode was
also prepared using these same materials and the
device retained its rectifying behavior in the presence
of the sensing gas and there is recovery upon gas
removal.
This work was funded by NSF under grants PREM
0934195 and RUI 0965023. References [1]C. Staii, A.T. Johnson, Jr., M. Chen, A. Gelperin Nano Lett. Vol. 5, No. 9, pp.
1774-1778 August 2005.
[2] F. Schedin , A. K. Geim , S. V. Morozov, E. W. Hill , P. Blake, M. I. Katsnel-son & K. S. Novoselov Vol.6, pp. 652 – 655 July2007
Table 1 Composite and pure SWNT’s sensors response time and recovery time
Sample PVDF-TrFE/SWNT’s SWNT’s
Sensing gas Acetone NO2 Ace-tone
NO
2 Response time(s) 5 200 15 180
Recovery time (s) 100 235 120 200
Page 6 Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Electrical Characterization of CVD Graphene
Yarelys Dávila
Advisor: N.J. Pinto
Graphene is a one atom thick carbon sheet that can be obtained via exfoliation of graphite or via chemical
vapor deposition (CVD). By using a very simple shadow masking technique, gold contact pads were evapo-
rated over the graphene thereby eliminating chemical etching that is required when using photolithography
and often leads to sample contamination. CVD graphene was electrically characterized in a FET configura-
tion under different experimental conditions that include UV exposure, gas sensing and temperature. Our
measurements yielded a carrier mobility of up to 3000 cm2/V-s for some devices. Exposure to UV dopes
graphene in a controlled manner. The doping level could be maintained indefinitely in vacuum or could be
completely reversed by slight heating in air without loss of device performance. The FET’s were also tested
at different temperatures with little change in the transconductance response. Exposure to ammonia gas
n-doped graphene while exposure to NO2 p-doped it. The figure below shows UV doping of CVD graphene.
(a) The conductivity (G) versus gate voltage (Vg) curves for different doping time, measured at room tem-
perature and a pressure of 10-2 Torr. Dotted lines are fitted line to obtain the carrier mobilities shown in the
inset table.
Electrical Characterization of Field Effect Transistors made from
C-nanotubes Covered with Poly(3-hexylthiophene)
Luis O. Pomales
Advisor: N.J. Pinto
Organic transistors were fabricated using a thin film of regio-regular poly(3-hexylthiophene-2,5-diyl) spun
from a 0.5 wt% solution in CHCl3 on doped Si/SiO2 substrates with and without CNT’s. The performance of
devices with percolating networks of CVD grown single-wall carbon nanotubes (SWNT’s) between the
source (S) and drain (D) electrodes and without SWNT’s are compared. Nanotubes are used as a way to
shorten the effective mean distance between the S/D terminals while retaining the wide spacing macroscopic
shadow mask technique for S/D fabrication. We found that devices made with SWNT’s do not exhibit S/D
current saturation but have a charge mobility of 1.2x10-2 cm2/V-s and an on/off ratio of 9, while the device
without SWNT’s show clear saturation with a charge mobility of 8.6x10-4 cm2/V-s and an on/off ratio of 870.
The devices made with nanotubes possess a larger off state current although they show a ~14X increase in
the mobility which can thus be increased without using sophisticated lift-off techniques to shorten the S/D
distance.
Número 7 Page 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Observation Report for the Year 2009,
Humacao University Observatory
D. Centeno, L. Rivera-Rivera, E. Franco, V. Maldonado,
M. De Jesús, R.A. Rodríguez, A.J. Sosa, M. Rosario, M. Díaz
Advisors: R. J. Muller and J.C. Cersosimo
We report measurements of position angle and separation of 120 binary stars observed during the year
2009. We obtained the data using the 31 inch NURO Telescope at the Anderson Mesa location of Lowell
Observatory near Flagstaff, Arizona, in May and September. We gathered the data using the 2K x 2K CCD
camera - NASACAM - at the prime focus of the telescope. The data was analyzed at the Humacao
University Observatory.
Número 7
Jean Carlo Serrano
Advisor: Rogerio Furlan
Micro- and nanofibers find applications in several areas, including electronics, chemistry, energy, biomedicine,
and textile, among others. Functional fibers or fibers with multi-compositions can be obtained by electrospin-
ning of polymeric solutions blended with additional compounds as, for example, nanoparticles, carbon
nanotubes, ceramics, etc. The incorporation of magnetic nanoparticles in fibers has been considered a topic of
interest, particularly in the case of iron (II, III) oxide (magnetite, Fe3O4). This is a material with magnetic,
catalytic, conductive, and biological properties. Also, the presence of these nanoparticles can be used to orient
the fibers during electrospinning, applying appropriately a magnetic field. In this work solutions were pre-
pared using 0.25 g of poly (ethylene oxide) (PEO, a bio-compatible polymer, Sigma Aldrich, molecular
weight: 2,000,000), 10 ml of chloroform (J. T. Baker, 1% ethanol) and different amounts (1.6% wt., 3.2% wt.,
6.2% wt., 12%wt., and 21% wt.) of iron oxide (II, III) nanopowder / nanoparticles (Fe3O4, 98+%, 20-30 nm,
US Research Nanomaterials, Inc.). In order to guarantee that the nanoparticles were completely dispersed, the
solutions were sonicated before deposition for 45 minutes. The electrospinning setup used electrodes made of
aluminum with dimensions of 5.0 cm x 2.5 cm x 1.2 cm. The electrode separation was 14 cm. Polymer was
injected inside the electric field by positioning the tip of a tuberculin syringe 2 cm above and 0.5 cm far from
the middle of the upper extremity of the positive electrode. A voltage between 20 kV and 25 kV was applied
to the positive electrode and the negative electrode was grounded. This modification of the conventional elec-
trospinning setup allows obtaining oriented fibers. The obtained fibers presented a good degree of orientation
and dimensions of micrometers. They presented regions with agglomerates of nanoparticles and their diameter
increased as the concentration of nanoparticles in the solution increased. Energy Dispersive Spectroscopy
(EDS) confirmed the agglomeration. Further studies will consider polymeric solutions with different concen-
trations and other types of polymers that can allow obtaining particles homogenously distributed in nanofibers.
Page 8 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Study of Formation of Polymeric Fibers Containing Magnetic Nanoparticles
Optical microscope image of a fiber collected on top of a silicon
substrate (12% wt. of Fe3O4; applied voltage of 25 KV
Page 9
Study of Formation of Polyvinylidene Fluoride Nanofibers Using
Acetone as Solvent
William Serrano García
Advisor: Rogerio Furlan
RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Número 7
This work addressed the formation of Poly (vinylidene difluoride) (PVDF, a Piezoelectric polymer) fibers to
be used as structural material for chemical sensors applications. The idea is to incorporate, further, other
materials, as Vulcan (carbon black) to obtain conductive nanofibers and copper phthalocyanine to improve
adsorption and electrochemical response. Solutions were prepared by weight per cent of PVDF and Ace-
tone. We used concentrations of 5, 10, 15 and 20wt%. Fibers were formed using electrospinning with the
following conditions: electrodes separation of 22-25 cm and applied voltage of 10 kV. For low concentra-
tions of PVDF (5wt %), only drops with a little formation of fibers were deposited on the collector
(aluminum foil). Increasing the concentration to 10 wt%, nanofibers and large beads are observed. For a
concentration of 15 wt%, homogeneous fibers with typical diameters approximately of 1µm - 4µm can be
obtained. Increasing further the concentration to 20 wt%, large agglomerates of polymer are observed with
the nanofibers. Thus, this preliminary study allowed us to establish process conditions for the continuation
of this work. For this purpose, a concentration of 15 wt% will be adopted.
5 wt%
10 wt%
15 wt%
20 wt%
Page 10
In this work we investigate the use of a novel ink containing polyacrylonitrile (PAN) and N, N dimethylfor-
mamide (as solvent) to define patterns using Atomic Force Microscopy (AFM). PAN is a largely used
polymer that has been explored as a precursor to obtain carbon nanofibers. Also block copolymers
containing PAN have been pyrolyzed to obtain well-organized nanostructured carbon materials. An AFM
(Digital Instruments, model Dimension 3100) was used to define polymeric squares on oxidized silicon
substrates covered with gold (~100 nm deposited by evaporation). The contact tips are prepared, for
writing, in the following manner: they are immersed in a solution containing 25 mg of PAN (average
molecular weight 150,000) and 5 ml of N, N dimethylformamide (DMF) for ten seconds and the excess
solution is allowed to run off. The tip is then rinsed in pure DMF for another ten seconds and allowed to
dry. Finally the tip is submerged once more in the PAN solution and allowed to dry. Once the tip is
mounted and focused, polymeric structures are defined and identified on the surface. The AFM is set up to
operate in contact mode using scan angle of 90°. Structures could be seen using friction images (scale
of .2V). The surface is scanned three times, twice to write the polymeric structure and once to read it. The
typical parameters used to write were: scan size 1µm, frequency 2Hz, deflection setpoint 4V. Larger
frequencies, and smaller scan sizes or deflection setpoints were sometimes used. The typical parameters
used to read were: scan size 5µm, frequency 4Hz, deflection set point 1V. These parameters were used to
successfully define and observe 1µm2 squares on a gold substrate. Once an image had been taken by the
AFM, it was flattened to enhance contrast. These conditions were based on results obtained using a 0.5
mM supersaturated MHA (mercaptohexadecanoicacid) solution with ethanol. Using this very known ink,
images of squares with 1 µm2 could be observed using friction mode (scale of 0.2 V). This work was
presented in NCUR 2012 and a paper was submitted for publication in the proceedings of this conference.
Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Writing Polymeric Patterns Using an Atomic Force Microscope
Godohaldo J. Pérez Medina
Advisors: Rogerio Furlan and Luis G. Rosa
Polymeric structure defined by writing two times a square area of 1µm2, using a frequency of 2Hz, and a
deflection set point of 4V. After reading (scan size 5µm, frequency 4Hz, deflection set point 1V) the
lateral dimensions of the polymeric structure defined were 0.96 µm by 1.01 µm.
Page 11
Study of Ionized Hydrogen in the Carina Region
Milennys Velázquez Flores, Clarissa Vázquez Colón, Grace Fontanes, Milzaida Sanabria
Advisor: J. C. Cersosimo, PhD.
Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
A typical characteristic of the Carina Nebula is its complex kinematical structure, which is observed in opti-
cal and radio lines. Due to the existence of many young and massive stars, there are considerable amounts of
ionized gas. By using observations of the atomic transition H166α radio recombination line (RRL) the
behavior of the kinematics of the ionized gas in the region was studied. In this work a grid of about 600 pro-
files, obtained with the Parkes Radiotelescope, has been analyzed. Each profile was processed in order to fit
a base line and after that a Gaussian fit was made for each position. The radial velocity resolution of the
profiles is about 4 km s-1 .
Finally, the region was mapped for different radial velocity at interval of 10 km s-1. A set of maps shows the
kinematics of the gas which suggests a shell like structure of ionized gas. It is apparent that the structure is
spatially correlated with the young open clusters Trumple 14. As a result it is suggesting that the ionized gas
is being blown out by the stellar wind of the young stars of the cluster.
Figure 1: Presentation at the Junior Technical Meeting.
From left to right: Milennys, Milzaida, Grace & Clarissa.
Page 12 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Número 7
Nanoscale Fabrication of the Ferroelectric Polymer Poly(vinylidene
Fluoride with Trifluoroethylene) P(VDF-TrFE) 75:25 Thin Films by Atomic
Force Microscope Nanolithography
Omar Vega, David Delgado, Freddy Wong, Rosette González
Advisor: Luis G. Rosa
Thin films of an organic ferroelectric system, poly(vinylidene fluoride with trifluoroethylene) P(VDF-
TrFE) 75:25 layers, have been deposited on highly ordered pyrolytic graphite (HOPG) and silicon
dioxide (SiO2) by the horizontal Schaefer method of Langmuir-Blodgett (LB) techniques. It is possible
to “shave” or mechanically displace small regions of the polymer film by using atomic force micro-
scope nanolithography techniques such as nanoshaving, leaving swaths of the surface cut to a depth of
4 nm and 12 nm exposing the substrate. The results of fabricating stripes by nanoshaving two holes
close to each other show a limit to the material “stripe” widths of an average of 153.29 nm and 177.67
nm that can be produced. Due to the lack of adhesion between the substrates and the polymer P(VDF-
TrFE) film, smaller “stripes” of P(VDF-TrFE) cannot be produced, and it can be shown by the
sequencing of nanoshaved regions that “stripes” of thin films can be removed.
Page 13 Número 7
RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Weak Screening of a Large Dipolar Molecule Adsorbed on Graphene
Lingmei Kong, G.J. Pérez Medina, J.A. Colón Santana, F. Wong, M. Bonilla,
Advisors: Luis G. Rosa, D.A. Colón Amill, L. Routaboul, P. Braunstein, B. Doudin, Chang-Mook Lee,
Jaewu Choi, Jie Xiao and P.A. Dowben
We compare the electronic structure of a quinonoid zwitterionic type molecule adsorbed on both gold and
graphene on copper substrates. This (6Z)-4-(butylamino)-6- butyliminio)- 3-oxocyclohexa-1,4-dien-1-
olate, C6H2(NHR)2(O)2 where R = n- C4H9, film is made of small molecules with a large intrinsic di-
pole of 10 Debyes. We find that the photoemission and inverse photoemission final states are well
screened for these dipolar molecules on gold. This is not observed when they are adsorbed on graphene
on copper. This weaker screening results in a larger highest occupied molecular orbital to lowest
unoccupied molecular orbital gap for the molecules on graphene.
The Effect of Thermal Annealing on the Efficiency of Semitransparent
Organic Solar Cells
Gabriel Calderón Ortiz, Héctor Carrasco Rodríguez, Jorge Marcano Bermúdez
Advisor: Josee Vedrine-Pauléus
Page 14 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Número 7
Most modern devices we use require some type of energy. The most common way to obtain this energy
comes from petroleum. This in turn creates an environmental problem because of emissions released into
the atmosphere. One of the ways to reduce the consumption and dependence on petroleum is to develop
and improve current alternative energy technologies.
Solar cells provide an alternative and environmentally friendly source of energy from the sun. In this work,
we fabricate organic solar cells and characterize their conduction under a simulated solar light source.
In our study, we analyzed the effect of annealing polymeric blends on cell efficiency while maintaining the
samples under ambient atmosphere. The organic cells have an active region composed of electron-donor
poly(3-hexylthiophene) (P3HT) and electron acceptor penyl-C61-butyric acid methyl ester (PCBM) mate-
rials to form a pn heterojunction. These organic polymers, with the addition of poly (3,4-
ethylenedioxythiophene) poly(styrenesulfonate (PEDOT:PSS) are used in thin films on an indium tin oxide
(ITO) coated glass substrate because it is a transparent conductor.
The fabrication process for making the solar cells is mostly carried out inside a vacuum chamber filled
with nitrogen gas to limit the effect of degradation on polymers from oxygen, heat, and humidity. We
attempted to find an optimal annealing temperature for P3HT:PCBM whereby the solar cell can generate
current with greater efficiency. The samples were annealed at these temperatures-80˚C, 100˚C, 120˚C and
140˚C. We investigated the effect of annealing on the solar cell efficiency by measuring their current-
voltage characteristics under the given conditions.
Our preliminary results show a correlation between solar cell efficiency and annealing temperature of the
P3HT:PCBM- as the temperature increases, solar cell efficiency decreases. We will continue further
experiments to determine efficiency at temperatures lower than 100 ˚C and at higher temperatures to
confirm this correlation.
Figure 1. Annealing temperature vs. Efficiency. Cell
efficiency was measured/calculated using the Keithley
IV Characterization software program. This graph shows
the data for the 100˚C-annealed cell when exposed to
simulated solar light.
Page 15 Número 7
RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
V. De La Rosa
Advisor: Ernesto P. Esteban
Radiation Hazards on Long-Haul Airplane Flights
The possible carcinogenic effects of galactic cosmic rays (GCR) on long-haul airplane flights are
investigated. To mimic a carcinogenesis process, we have modified the mathematical Jones model of
radiation-induced myelopoiesis by adding new compartments corresponding to mutated and cancerous
cells populations. This new biomathematical model can be written in terms of a set of non-linear
differential equations.
At different Earth's altitudes and latitudes, we assume n mutations and a given cosmic ray dose rate, to
estimate the evolution of cell survival curves and cancerous cell populations. Two applications are
considered.
First, we found that regardless of latitude there is no cosmic rays carcinogenic effects on the airplane's
crew, when flying during 20 years (100 hours/month) at altitudes less than 60000 ft. However, if the
altitude increases and the flight is nearer Earth´s poles, a carcinogenesis process could be initiated.
Second, we considered an actual flight from New York to Athens, and found that the evolving cancer
cell population can be quantified at any given time t by a linear quadratic and quartic relationship.
Pilots flying in this route 40 years (100 hours/month) could be at cancer risk at the end of their careers.
Page 16 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Número 7
On the Carcinogenic Effects of Galactic Cosmic Rays at
Low Earth Orbit and Deep Space
P. Agosto
Advisor: Ernesto P. Esteban
By necessity and curiosity humans destiny is to colonize and to habitat other planets. In doing so, one of
the challenging problems is to understand, to estimate, and to mitigate the carcinogenic effects of galactic
cosmic rays (GCR) on humans.
We have developed a simple but not trivial biomathematical model to estimate the possible carcinogenic
effects of the interaction between CGR and astronauts’ tissue. This deterministic model was built on top
of the experimental and theoretical work done by Jones et al [1], and it does not neglect microgravity
effects.
Two radiation environments were studied. At the International Space Station (ISS), it is estimated that
only after eleven consecutive mission’s astronauts cancer risks will increase. However, for the interplane-
tary travel from Earth to Mars, a cancer initiation process could begin as soon astronauts arrive to Mars.
ISS exposed to GCR In Fig. 1, survival curves look similar except for the first expedition. The GCR irra-
diation effects on tissue are more harmful beginning the second flight. Notice also, that sub-lethal repair is
very efficient. ISS astronauts fully replenish normal cells in about two months. The cancer cell popula-
tion is given in Fig. 2. The cancer threshold (0.00025) is reached at about 175 months. This implies that
increasing cancer risks for astronauts at the ISS is negligible.
10 20 30 40 50 60 70months
0.9700.9750.9800.9850.9900.9951.000
S
Survival .Curve
50 100 150 200Months
0.0001
0.0002
0.0003
0.0004
Nc
Cancerous Cell Population.for.Fcc 50 Fnn
Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Page 17
Polyaniline-Carbon Nanotubes Composite Actuator
Sabrina Rosa and Carlos Camargo
Advisors: Idalia Ramos, University of Puerto Rico at Humacao; Barcelona, Spain; Eva Campo,
University of Pennsylvania; Jaume Esteve, Centre Nacional de Microelec-tronica, Barcelona, Spain
The understanding of photoactuation in Carbon Nanotubes (CNT)-polymer composites can contribute to
the development of micro-and-nano-optical-mechanical systems for applications that include intracellu-
lar motors, artificial muscles, and tactile displays for blind people. The integration of CNTs into
polymers combines the good processability of polymers with the functional properties of CNTs. CNTs-
polymer composite fibers were fabricated using the electrospinning technique. Electrospinning process
orients the CNTs along the precursor stream and can contribute to enhance photo actuation properties.
The addition of polyaniline, an electroactive conductive polymer is expected to enhance the actuation
strain of the composite. Aim of this research is to study photoactuation in MWCNT-Polyanilile electro-
spun fibers. Fibers were characterized using Scanning Electron Microscopy, Atomic Force Microscopy,
and X-Ray Diffraction. Results demonstrate evidence of photo-actuation after irradiating the fibers with
visiblelight. Tests are being conducted to understand the mechanisms of the composites response to light
stimulation.
Research Sponsored by Partnership for Research and Education in Materials (NSF-DMR 0934195).
Page 18 Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Aluminum Nitride Nanofibers Fabricated Using
Electrospinning and Nitridation
Xenia Barbosa
Advisors: Idalia Ramos, University of Puerto Rico at Humacao,
Eva Campo and Jorge Santiago, University of Pennsylvania
Aluminum Nitride (AlN) and other nitride semiconductors are important materials in the fields of optoelec-
tronics and electronics. AlN nanofibers were synthesized using electrospinning and subsequent heating
under N2 and NH3 atmospheres. The precursor solution for electrospining contains aluminium nitrate and
cellulose acetate. The electrospun nanofibers were heated in N2 to eliminate the polymer and produce
Al2O3, and then nitridized at a temperature of 1200ºC under NH3 flow. Scanning Electron Microscopy
(SEM) observations demonstrate the production of fibers with diameters ranging from a few nanometers to
several micrometers. X-Ray Diffraction and UV-VIs analyses show the production of AlN nanofibers with
hexagonal wurzite structure and a band gap of approximately approximately 6 eV. Current-Voltage
measurements on a single AlN fiber with gold electrodes suggest the formation of a Schottky contact.
The fabrication method and results from the fibers characterization will be presented.
This work was funded by NSF-DMR-0934195
Synthesis of Electrospun Indium Gallium Nitride Nanofibers
Joshua L. Robles-García
Advisor: Idalia Ramos
InGaN is a novel material for the development of optoelectronic devices because its band gap can be chan-
ged from 3.4 eV to 0.7 eV by varying the indium concentration. InGaN nanofibers have been produced
using the electrospinning technique and a precursor solution composed of indium nitrate (III), gallium
nitrate (III), and cellulose acetate dissolved in dimethylacetamide and acetone. After electrospinning the
fibers are sintered in nitrogen at 400°C to decompose the polymer and the nitrates. Then, they are nitridi-
zed at 650°C under an ammonia gas flow to complete the production InxGa1-xN, were x is the InN molar
fraction and varies as 0.25, 0.5 and 1. GaN (x=0) nanofibers produced in previous work and sintered at
900°C are used for comparison. Scanning Electron Microscopy (SEM) show the production of long and
continuous fibers with diameters of hundreds of nanometers and up to a few micrometers. X-ray
Diffraction (XRD) analysis of the fibers shows the production of fibers with wurtzite InN and GaN peaks.
Ultraviolet-visible (UV-Vis) spectra were obtained to analyze the changes in band gap with In concentra-
tion. The band gap of the electrospun InxGa1-xN fibers varies from 3.4 nm for x=0 (GaN) to 2.2 nm for x=1
(InN).
RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Page 19 Número 7
Renovable Energy From Waves Using Magnetic Induction
Carlos Calderón and Kenneth Benítez
Advisor: Juan A. González Sánchez
The purpose of this project is to apply the principle of magnetic induction, constructing an acrylic box in
order to convert mechanic energy into electromotive force (EMF) from the ocean wave shock. First we
started testing with different springs to determine an efficient way to increase the impact of the oscillation
caused by the waves.
Figure 1. AutoCAD Design of the Renovable Energy Device
Voltage vs. time results were
plotted using HPVEE data
acquisition software and
strength tests were performed
to find the best spring constant
using Hooke's law. We chose
6500 Gauss axial cylindrical
neodymium magnets.
After that we started to design the box using
AutoCAD, taking into account the center of
mass calculations. To complete the design and
construction 3 inches in diameter coils with
1000 turns were placed. Finally, we tested our
machine on the beach and the pool of UPR-H
campus.
Figure 2 Voltage vs. Time on the first wave of impact
RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Page 20 Número 7
Approaching an Organic Semi-metal: Electron Pockets at the Fermi Level
for a pbenzoquinonemonoimine Zwitterion
Zhengzheng Zhang, José Alvira, Omar Vega, Gerson Díaz, Julian Velev
Advisors: Luis G. Rosa, Lucie Routaboul, Pierre Braunstein, Bernard Doudin, Yaroslav B. Losovyj and
Peter A. Dowben
There is compelling evidence of electron pockets, at the Fermi Level, in the band structure for an organic
zwitterion molecule of the p-benzoquinonemonoimine type. The electronic structure of the zwitterion
molecular film has a definite, although small, density of states evident at the Fermi level as well as a
nonzero inner potential and thus is very different from a true insulator. In spite of a small Brillouin zone,
significant band width is observed in the intermolecular band dispersion. The results demonstrate that
Bloch’s theorem applies to the wave vector dependence of the electronic band structure formed from the
molecular orbitals of adjacent molecules in a molecular thin film of a p-benzoquinonemonoimine type
zwitterion.
El cráter Giordano Bruno (GB) de 22km de diámetro esta ubicado en las coordenadas (Lat: 35.96, Lon:
102.86) correspondiente a la cara opuesta de la Luna. De aparente reciente formación, Hartung (1976)
sugirió que el mismo se formó en la edad media y fue responsable de la explosión del 18 de junio de 1178
reportado por el monje e historiador ingles Gervasio de Canterbury. Morota et al. (2009), usaron imágenes
de la sonda japonesa SELENE (Kaguya), y el modelo de Nukum et al. (1983), para estimar la edad del
cráter en unos 4 millones de años. Joven geológicamente pero no es histórico.
Nosotros aplicamos el mismo método de conteo de cráteres pequeños en el suelo nuevo alrededor del cráter
pero usando el modelo de Bruckman et al. 2007, el cual contempla una tasa mayor de impactos en el
número acumulativo, N(>D) = A τ D -3.3 /3.3, debido a el coeficiente A, el cual es significativamente
mayor. Dicho coeficiente esta basado observaciones de Poveda et al, (1999) y mediciones del número acu-
mulativo de bólidos en la atmosfera terrestre (Silber et al. 2009). Para una superficie no saturada, N(>D)
= Φ τ, donde Φ es el flujo acumulativo de impactos y τ es el tiempo que ha estado expuesta recibiendo
impactos.
En la figura a continuación se muestra una imagen del Lunar Reconnaissance Orbiter donde se amplía parte
del suelo recién formado con cráteres nuevos alrededor del GB. El área total de contaje para cráteres de
>200m fue de 960km2. Para los cráteres >100m, el área total fue de 240km2. Para cráteres >50m y
>25m, el área fue 60km2 y 15km2, respectivamente. La región de conteo se dividió en 21 parcelas de
45.7km2 en la cual se contaban todos los cráteres mayores a 200m. Luego se hace un acercamiento en la re-
gión central, con la siguiente resolución que representa un área 11.4km2 para contar los cráteres de 100m.
Así sucesivamente para los de 50m y 25m con un área de conteo de 2.85km2 y 0.71km2,, respectivamente.
Este proceso se repitió en las 21 parcelas lo que asegura que los 4 tipos de cráteres contados se distribuyen
uniformemente en toda la región.
La Edad del Cráter de Giordano Bruno
Page 21
Luis O. Pomales
Advisors: Abraham Ruiz y William A. Bruckman
Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65
Page 22 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Número 7
La edad estimada para el cráter de GB fue de 92,000 ± 46,000 años. Esa sería un valor máximo para la edad
debido a la posibilidad de contaminación por cráteres secundarios. En este caso la contaminación es poco
probable por ser un impacto geológicamente joven. La incertidumbre en la edad proviene principalmente de la
calibración del modelo con los datos de Grive y Shomaiker (1994). A continuación se muestra la relación de
Número Acumulativo vs. Diámetro para cráteres mayores de 25m, 50m, 100m y 200m. La pendiente de 3.48
nos confirma que es una superficie no saturada cuyo número de cráteres N (>D) esta determinada por Φ τ .
Definitivamente el cráter de GB no es el responsable del evento reportado en 1178.
Es extremadamente joven pero no histórico.
Sin embargo, hemos identificado otro cráter de poco más de 4km de diámetro, llamado provisionalmente,
cráter Rafael Muller (RM), en la posición Lat -32.99, Lon -4.47 a 390km al Noreste del cráter de Tycho. La
figura a continuación presenta una imagen del cráter y parte de su región alrededor ampliada a la misma
escala que en el GB. Al comparar ambas regiones es fácil ver que en el RM hay menos cráteres y son más
pequeños que en el GB, por consiguiente es más joven.
El conteo de cráteres en esa región nos permite establecer, según el modelo (Bruckman et al. 2009) su edad
en unos 640 años ± 320 anos. Considerando las incertidumbres, podemos señalar que este cráter es un buen
candidato para ser el responsable de la alega explosión en la Luna reportada hace 834 años.
Page 23 RESULTADOS DE INVESTIGACIONES SUBGRADUADA
REALIZADA EN LOS CURSOS FISI 4161-65 Número 7
Además de la coincidencia cronológica, el RM resuelve un problema que no ha sido explicado satisfactoria-
mente por los que proponen que el cráter de GB es responsable del evento de 1178. Un cráter tan grande
como ese removió cerca de 900km3 material de las cuales 10 millones de toneladas alcanzaron la Tierra
(Gault and Schultz, 1991) causando una lluvia de estrellas sin precedente por varias semanas (Withers,
2001). Hasta el momento no se ha encontrado registros históricos ni evidencias geológicas que den cuenta
de tan fenomenal lluvia de estrellas en esa época. Por otro lado un impacto de 22km de diámetro en la Luna
o la Tierra es poco probable. Según los modelos mas usados son uno cada dos millones de anos. Según el
modelo de Bruckman et al. (2012) la tasa de impactos para cráteres de 22 km es de 3 por cada millón de
años.
Por otro lado, el cráter RM excavó casi 300 veces menos que el GB, por lo que el material transferido a la
Tierra y la consecuente lluvia de estrellas, se reduce en ese mismo orden. El cráter RM tuvo una potencia
de más de 300MT y excavó cerca de 3km3 de material. El polvo levantado, sin duda fue suficiente para
reflectar la luz del Sol hacia la cara oscura de la Luna, iluminando parte del disco, consistente con lo
reportado por Gervasio de Canterbury.
Referencias:
Bruckman, W. A., Ruiz, A., and Ramos, E. RevMex (Series de Conferencias) Vol. 35, p.19. (2009)
Bruckman, W. and A., Ruiz, A., (2012) en preparación.
Grive and Showmaker, E., 1994: The record of Past Impacts on Earth, T. Gehrels, Editor: University of Ari-
zona Press.
GAULT D. E. AND SCHULTZ P. H. (199 1) Ejecta from lunar impacts:
Where is it on Earth? Meteoritics 26, 336-337.
Hartung, J. B. (1976) Was the Formation of a 20-km-Diameter Impact Crater on the Moon Observed on
June 18, 1178? Meteoritics, v. 11(3), p. 187-194
Morota, T., Haruyama, J., Miyamoto, H., Honda, C., Ohtake, M., Yokota, Y., Matsunaga, T., Hirata, N.,
Demura, H., Takeda, H., Ogawa, Y., and Kimura, J. (2009) Meteoritics and Planetary Science, v. 44(80),
p. 1115-1120.
Poveda, A., Herrera, M. A., et al. 1999, Planet. Space Sci., 47, 679
Withers, P., Meteoritics and Planetary Science, v. 36(4), p. 525-529 (2001)
Nota de los editores
La inclusión de la investigación y la labor creativa son fundamentales para el
desarrollo integral de los estudios subgraduados. Los miembros del Departa-
mento de Física y Electrónica reconocen la importancia de estos elementos
como parte fundamental de la labor académica. La aplicación del conoci-
miento en la búsqueda de nuevas verdades y la interpretación del mundo que
nos rodea, permite el desarrollo del pensamiento crítico; es una herramienta
académica innovadora para motivar y satisfacer la curiosidad intelectual del
los/las estudiantes. Además contribuye al desarrollo social y cultural
agilizando la inserción en el ciclo económico de Puerto Rico y del mundo.
La inmersión de estudiantes en investigación subgraduada se hace desde los
inicios del programa de Bachillerato de Física Aplicada a la Electrónica, en
1987, mediante el ofrecimiento del curso Investigación Subgraduada (FISI
4161). La usual contratación de Profesores con peritaje en investigación
capturó el interés de los estudiantes de Bachillerato para involucrarse en tan
digna tarea. El esmero y dedicación de los profesores ayudó a ellos mismos
a trasformar las técnicas de enseñanza debido al desafío que implica investi-
gar y formar a estudiantes en la disciplina.
La consecuencia de estos esfuerzos condujo a aumentar el ofrecimiento
debido al interés de los estudiantes en hacer investigación. En consecuencia
se atendió la demanda de los estudiantes, incluyendo los curso de Investiga-
ción Subgraduada (FISI 4162 FISI 4163 y FISI 4164). Los cuatro cursos
mencionados se ofrecen regularmente desde agosto de 1993. El compromi-
so permitió a la academia refinar las estrategias de enseñanza-aprendizaje,
que en esencia son el modelo tomado por el constructivismo, el método de
prueba y error.
Después de veinticuatro años de esfuerzo, el Departamento cuenta con una
decena de profesores que escriben propuestas, consiguen fondos externos y
hacen presentaciones en reuniones internacionales de ciencia, y publican
periódicamente en revistas de circulación internacional. En el Departamento
hay tres laboratorios dedicados a la investigación y un laboratorio de instruc-
ción equipado con instrumentos de primera línea en el que se ofrecen dos
cursos de concentración. También otras facilidades de investigación son los
recursos del Observatorio Astronómico de Humacao, en el cual la prepara-
ción obtenida por los estudiantes les facilita tener opción de seguir estudios .
Vale destacar el compromiso de la Institución (UPRH) que hace posible la
investigación subgraduada, es por ello que me complace reconocer a las
diferentes administraciones que están y han colaborando en este esfuerzo.
El reconocimiento es también extendido a los profesores por la labor de
adiestramiento a los estudiantes. La revista de investigación subgraduada fue
concebida para que sea un instrumento administrativo que permita la visibili-
dad de esta actividad, pero además es un documento dirigido a los estudian-
tes, profesores y la comunidad científica de Puerto Rico, con el propósito de
divulgar las actividades académicas que han sido pioneras en el Sistemas
UPR junto con otros Recintos. Este instrumento estará además disponible en
la Internet para permitir el acceso a todas las comunidades.
Proyectos Auspiciadores:
1. Puerto Rico Space Grant Consortium (NASA)
2. Puerto Rico Alliance for Minority Participation (LSAMP)
3. NSF
- Penn-UPR Partnership for Research and Education in Materials (DMR-0353730)
- Research in Undergraduate Institutions ( RUI)
5. RISE Program at UPRH
6. PRIDCO
Universidad de Puerto Rico en Humacao
Departamento de Física y Electrónica
Call Box 860
Humacao PR 00792
www.uprh.edu/fisica
Tel. 787-850-9344-9381 Fax: 787-850-9308
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